Let's take your claims at face value and see if your conclusion makes sense. SL merchants assume that people already bring a lot of copybotted content from SL to OpenSim. The accepted narrative being that if you're successful in SL then your content is being illegally distributed all over OpenSim-based grids. This is without merchants ever offering their items for sale in any OpenSim based grid - the items are being taken from inside SL.
What we're claiming is that if your content is already being illegally distributed then the people currently profiting from that distribution aren't you. The only way you can make any money in this "1800's Wild Wild West" is getting some of the people using OpenSim to buy from you instead of getting your content from other sources. Not selling to those people won't help you protect your content, it will just cost you sales you could have made.
The way to do that is to use a convenient marketplace and price your content reasonably. This is the conclusion the music industry got to after years of trying to combat illegal music pirating on the Internet. Initially they tried to sell music with content protection (DRM) but they soon realized that they could make more money selling DRM-free music in iTunes instead.
SL content creators should consider the success of iTunes selling DRM-free music as a case study for profiting from selling content to people who can easily get that content for free in other websites. If you believe your content is going to be illegally distributed then make sure to offer a convenient way for everyone who wants that content to buy it from you instead.